Reachable assertion in nats-server - #VU135932
Published: June 30, 2026
Vulnerability identifier: #VU135932
CSH Severity: Medium
CVSS v4.0: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N/E:U/U:Green
CVE-ID: N/A
CWE-ID: CWE-617
Exploitation vector: Remote access
Exploit availability:
No public exploit available
Vendor: NATS - The Cloud Native Messaging System
Affected software:
nats-server
nats-server
Detailed vulnerability description
The vulnerability allows a remote attacker to cause a denial of service.
The vulnerability exists due to reachable assertion in JWT claim processing in operator-mode authentication when processing a malformed client JWT issuer key. A remote attacker can send a specially crafted JWT containing a truncated public account key to cause a denial of service.
Only operator-mode deployments using JWT authentication are vulnerable, and the issue can be triggered before authentication completes.
Remediation
Install security update from vendor's website.